1. Field of the Invention
This invention relates to a process for upgrading heavy hydrocarbon oils, and more particularly to improvements in the hydrogen donor diluent cracking process for converting heavy oils such as vacuum residua from a petroleum refinery, coal extracts, oil from oil shale and bitumen from tar sands to more valuable lighter liquid distillates by thermally cracking the heavy oils in the presence of a hydrogen donor diluent.
2. Brief Description of the Prior Art
The hydrogen donor diluent cracking process in which certain low value hydrocarbon fractions are upgraded by thermal cracking in the presence of a hydrogen donor diluent is described in detail in U.S. Pat. No. 2,953,513. Process variables and operating conditions for the hydrogen donor diluent cracking process are discussed at length in that patent. One disadvantage of the conventional hydrogen donor diluent cracking process is that fractionation of the product stream from the cracking step produces a heavy bottoms or pitch stream which is of low value relative to the other products from the process and in some cases presents a disposal problem. A portion of this heavy pitch material may be recycled through the process, but as a practical matter a substantial purge is usually required in order to operate the process continuously in an efficient manner. A second disadvantage of the conventional hydrogen donor diluent cracking process is the requirement of a substantial amount of expensive hydrogen for hydrogenation of the donor solvent. The process of the present invention overcomes both of the aforementioned disadvantages, and provides a more efficient and more environmentally-acceptable process.
It is known in the art that hydrogen-rich reducing gases can be prepared by a non-catalytic controlled partial oxidation of hydrocarbon materials. Such a process is described in detail in Chemical Engineering Progress, Volume 57, No. 7, pp. 68-74. As described in that article, the oxidizing gas may be air, oxygen, or enriched air. The products from the partial oxidation process consist largely of hydrogen and carbon monoxide, and if a substantially pure hydrogen stream is desired the carbon monoxide and hydrogen can be passed to a shift converter to produce additional hydrogen according to the well-known shift reaction.
It is further known in the art that hydrogen-containing gases produced from partial oxidation processes can be utilized in various hydrocarbon refining steps which require hydrogen. U.S. Pat. Nos. 2,847,306; 3,756,944 and 3,764,547 are exemplary of patents describing hydrocarbon processing steps in which a reducing gas obtained by partial oxidation of a hydrocarbon material is utilized in subsequent processing.